The benefits of soy protein are well documented. According to nutritional studies, a diet rich in soy proteins can reduce serum cholesterol levels in humans. It has also been suggested that soy protein consumption leads to a reduced risk of illness and disorders such as osteoporosis, colon cancer, and prostate cancer. Thus, soy proteins and products including soy proteins provide significant health benefits.
Many foods and beverages are fortified with supplemental protein derived from soybeans. Native protein materials derived from soybeans, however, cannot be used effectively as a supplement in certain beverages and food compositions in which nutritional fortification is desirable, such as acidic beverages. Exemplary acidic beverages include carbonated and non-carbonated soft drinks, juices, and sports drinks. These acidic beverages generally have pH levels at which unmodified soy protein materials are substantially insoluble.
Adding unmodified soy protein materials to acidic beverages typically results in cloudiness and sedimentation. The result is a consumer product that has an undesirable appearance after being stationary for a period of time, such as on the grocery store shelf or in a consumer's refrigerator or pantry. Additionally, the consumer is required to shake or otherwise agitate the product prior to consumption in order to resuspend or redissolve the soy protein material contained therein. Even with significant agitation, not all of the soy protein material in the beverage may be resuspended or redissolved in the product. Thus, the consumer may not feel that they are receiving the full benefits of the soy protein present in the beverage, because they are not able to drink the sediment stuck to the bottom and sides of the container.
It is generally known in the art to modify soy protein materials by hydrolyzing the soy protein. Soy protein hydrolysates are commonly used to form nutritional acidic beverages, since soy protein hydrolysates are relatively more soluble in acidic aqueous solutions than unmodified soy protein. Soy protein materials are often hydrolyzed by treatment with proteolytic enzymes under conditions at which the enzyme hydrolyzes the soy protein into intermediate-length peptides. These intermediate-length peptides are relatively more soluble in acidic solutions than unmodified soy protein materials are, and have been frequently used as supplements in consumer applications such as acidic beverages. For example, in U.S. Pat. No. 3,897,570, Yokotsuka et al. describe a process for providing an acidic beverage containing soy protein wherein a slurry is formed of soy protein material, the slurry is heated by steam under pressure to denature the soy protein in the slurry, and the soy protein is hydrolyzed with an acid protease at a pH of 2.5 to 6.0 so the ratio of formol state nitrogen to total nitrogen in the slurry filtrate is less than 20%, thus preventing over-decomposition of the soy protein material. Yokotsuka et al. then filter a clear portion of the slurry and add it to an acidic beverage.
In addition to possessing good suspension stability, the food or beverage application containing soy protein must have good flavor. Generally, the hydrolysis of soy protein into intermediate-length peptides is preferred. This is due to the fact that soy protein is typically more soluble in acidic solutions, and also because the presence of short chain peptides often results in a soy protein product with a bitter, undesirable flavor. For example, in U.S. Pat. No. 3,846,560, Hempenius et al. describe a process wherein a slurry of soy protein material is hydrolyzed with a proteolytic enzyme, preferably at a neutral pH, whereby the process is terminated before it reaches the point of producing a significant amount of products with a bitter taste. Hempenius et al. then remove the precipitated material from the hydrolyzed soy protein slurry to obtain a clear soy protein solution for use in preparing an acidic beverage.
As can be seen from the foregoing, there is a need for a soy protein isolate having good suspension stability and flavor suitable for use in food and beverage applications, and specifically in acidic beverages.